1. Field of the Invention
This invention relates to copper alloys having high strength, good formability and relatively high electrical conductivity. More particularly, the crystalline grain structure of a phosphor-bronze is refined by an iron addition.
2. Description of Related Art
Throughout this patent application, all percentages are given in weight percent unless otherwise specified.
Commercial phosphor-bronze contains from 1%-10% tin, from 0.03%-0.35% phosphorous and the balance copper. These alloys have excellent cold processability, high tensile strength, high yield strength and good formability. The alloys are particularly suited for applications requiring repetitive motion or stress such as fasteners, electrical connectors, springs, electrical switches and wire brushes.
The use of phosphor-bronze is limited because the alloys are prone to cracking during hot working, such as rolling at elevated temperature. In addition, the electrical conductivity of the alloys is rather low. Copper alloy C51000, (nominal composition 94.9% copper, 5% tin and 0.1% phosphorus) has an electrical conductivity of approximately 15% IACS at 20.degree. C. IACS refers to conductivity as defined by the International Annealed Copper Standard and rates "pure" copper as having an IACS of 100% at 20.degree. C.
It is known that the addition of iron to phosphor-bronze improves the hot working characteristics of the alloy. U.S. Pat. No. 2,128,955 to Montgomery discloses the addition of 0.25%-5% iron to a phosphor-bronze containing 2%-20% iron. U.S. Pat. No. 4,249,941 to Futatsuka et al. discloses a copper alloy for electrical applications containing 0.5%-1.5% iron, 0.5%-1.5% tin, 0.01%-0.35% phosphorous and the balance copper. Futatsuka et al disclose that increasing the iron content above 1.5% results in degradation of the elongation capability and of the electrical conductivity.
Japanese patent application number 57-68061 by Furukawa Metal Industries Company, Ltd. discloses a copper alloy containing 0.5%-3.0%, each, of zinc, tin and iron. It is disclosed that iron increases the strength and heat resistance of the alloy.
While the benefit of an iron addition to phosphor-bronze is known, iron causes problems for the alloy. The electrical conductivity of the alloy is degraded and processing of the alloy is impacted by the formation of stringers. Stringers form when properitectic iron particles precipitate from liquid prior to solidification and elongate during mechanical deformation. Stringers are detrimental because they affect the surface appearance of the alloy and can change the formability characteristics.
There exists, therefore, a need for an iron modified phosphor-bronze alloy that does not suffer from the stated disadvantages of reduced electrical conductivity and stringer formation.